Oxidation of secondary and tertiary alkyl aromatic hydrocarbons

ABSTRACT

1. IN A PROCESS FOR THE OXIDATION OF SECONDARY AND TERTIARY ALKYL AROMATIC HYDROCARBONS WITH OXYGEN OR AN OXYGEN-CONTAINING GAS AT TEMPERATURES OF FROM 80* TO 130* C. IN THE PRESENCE OF A CATALYST TO PRODUCE THE CORRESPONDING HYDROPEROXIDE COMPOUNDS, THE IMPROVEMENT WHICH COMPRISES OXIDIZING SAID ALKYL AROMATIC HYDROCAR: BONS HAVING THE FORMULA   R1-CH(-R)-AR   IN WHICH R IS A LOWER ALKYL GROUP HAVING FROM ONE TO SEVEN CARBON ATOMS; R1 IS HYDROGEN OR A LOWER ALKYL GROUP HAVING FROM ONE TO SIX CARBON ATOMS; R AND R1, TAKEN TOGETHER, FORM A CYCLOALKYL RING HAVING FROM FOUR TO SEVEN CARBON ATOMS; AND AR IS PHENYL OR NAPHTHYL, IN THE PRESENCE OF A CATALYST COMPRISING A CUPROUS HALIDE SELECTED FROM THE GROUP CONSISTING OF CUPROUS CHLORIDE, CUPROUS BROMIDE, AND CUPROUS IODIDE, AND AN AROMATIC HETEROCYCLIC AMINE SELECTED FROM THE GROUP CONSISTING OF PYRIDINE, QUINOLINE, ISOQUINOLINE, TRIAZINE AND PYRAZINE, WHEREIN THE RATIO OF CUPROUS HALIDE TO AMINE IS IN TTHE RANGE OF ABOUT 1 TO 100 PARTS BY WEIGHT OF SAID HALIDE FOR EACH 100 PARTS OF AMINE.

3,845,140 OXIDATION OF SECONDARY AND TERTIARY ALKYL AROMATIC HYDROCARBONS Arthur M. Brownstein, Cherry Hill, N.J., and David L.

Kerr, Wilmington, Del., assignors to Sun Research and Development Co.,Philadelphia, Pa.

No Drawing. Continuation of application Ser. No. 709,786, Mar. 1, 1968.This application Mar. 10, 1970, Ser. No. 17,048

Int. Cl. C07c 73/ 08 US. Cl. 260-610 B 10 Claims ABSTRACT OF THEDISCLOSURE Cuprous halide which has been activated by contact with anaromatic heterocyclic amine is found to be an eifective catalyst forincreasing the rate of oxidation of secondary and tertiary alkylaromatic hydrocarbons such as cumene or ethylbenzene to form thecorresponding hydroperoxide.

CROSS-REFERENCE TO RELATED APPLICATION This application is acontinuation of US. Ser. No. 709,786, filed Mar. 1, 1968, in the name ofArthur M. Brownstein and David L. Kerr.

BACKGROUND OF THE INVENTION This invention relates to a process for theoxidation of secondary and tertiary alkyl aromatic hydrocarbons to formthe corresponding hydroperoxide. More particularly, this invention isdirected to increasing the rate of oxidation of such compounds as cumeneor ethylbenzene to form the corresponding hydroperoxide compound,

wherein there is employed as the oxidation catalyst a metallo-organiccomplex formed by reacting a cuprous halide with an aromaticheterocyclic amine.

It is known that cumyl hydroperoxide can be produced very slowly byauto-oxidation when air or oxygen is rapidly passed through cumenewarmed to about 80 C. Also, Canadian Pat. No. 510,517 teaches that therate of oxidation of cumene can be enhanced when carried out in thepresence of alkali or alkaline earth metal oxides or hydroxides, or inthe presence of salts and oxides of heavy metals. Under theseconditions, the conversion rate is only about 23% per hour.

The oxidation of cumene using metallic copper as the oxidation catalystis taught by US. Pat. 2,749,368. There is no teaching or suggestion inthis patent of the use of copper salts together with an amine as anoxidation catalyst.

SUMMARY OF THE INVENTION It has now been found, in accordance with thepresent invention, that secondary and tertiary alkyl aromatichydrocarbons can be oxidized at effective rates of conversion to formthe corresponding hydroperoxides when a complex formed by reacting acuprous halide with an aromatic heterocyclic amine is employed as theoxidation catalyst.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cuprous halide-aminecatalyst may readily be prepared in accordance with the teachingscontained in US. Pat. 3,219,625, as, for example, by reacting a cuproushalide with an excess of an aromatic heterocyclic amine such aspyridine, quinoline, isoquinoline, triazine, pyrazine or the like, andthereafter recovering the resultant complex from solution.Alternatively, and more preferably, the catalyst may be prepared in situby adding a slight United States Patent O 3,845,140 Patented Oct. 29,1974 "ice excess of amine to the cuprous halide in the reaction medium.The cuprous halide may be cuprous bromide or iodide, but is preferablycuprous chloride.

While the weight ratio of cuprous halide to hetero cyclic amine is notcritical, it is desirable that the catalyst contains from about 1 to 100parts by weight of cuprous halide for each 100 parts of amine, andpreferably from 5 to 30 by weight of cuprous halide, in order to provideoptimum effectiveness.

The secondary and tertiary alkyl aromatic hydrocarbons employed as thestarting materials in the process of this invention have the followingstructural formula:

wherein R is lower alkyl; R is lower alkyl or hydrogen; Ar is asubstituted or unsubstituted aromatic nucleus such as phenyl ornaphthyl; and R and R taken together form a cycloalkyl ring having from4 to 7 carbon atoms; and wherein R and R may be the same or differentalkyl groups. The aromatic nucleus may be substituted by such groups aslower alkyl, lower alkoxy, halo, nitro, or cyano radicals. Preferably,the secondary or tertiary alkyl aromatic is represented by suchcompounds as cumene or ethylbenzene, although it is understood thatcompounds such as p-diisopropylbenzene, sec.-butylbenzene,isopropylnaphthalene, p-cymene, and the like may also be utilized.Moreover, it has been found that this process is equally effective inoxidizing cycloalkyl aromatics such as phenylcyclohexane. Thus, forpurposes of this invention cycloalkyl groups which are substituted for Rand R taken together, react as tertiary alkyl compounds.

The process of this invention utilizing the aforedescribed catalyst, isconveniently carried out by the rapid passage of oxygen or air through asuitable reactor, to which has first been added a solution of the alkylaromatic and the cuprous halide-heterocyclic amine catalyst. The air oroxygen should be brought into intimate contact with the liquid phase,for example, by the use of high speed stirrers, suitable nozzles or thelike.

The amount of catalyst employed will vary depending upon the nature andamount of material to be oxidized. In general, however, the amount ofcatalyst may vary from about 0.05 grams to 0.8 grams of catalyst permole of substrate.

The rate of input of oxygen or air will depend upon the temperature andpressure utilized during the oxidation. There should be provided atleast an amount theoretically sufficient to convert thealkyl-substituted aromatic compound completely to the correspondinghydroperoxide, and preferably an excess of this amount. It has beenfound that a fiow rate ranging from 0.5 to 300 liters per hour isgenerally sufficient for most conversions. Any uncombined oxygen may, ofcourse, be recycled to the reactor. The reaction may be effected atnormal or superatmospheric pressure.

The reaction temperature may range from about 130 C. but is preferablyin the range of -1 15 C. While it has been found that the rate ofconversion of substrate to hydroperoxide may initially be increased attemperatures over about C., this is accomplished only at the expense ofsome of the remaining substrate which is converted into unwantedby-products.

The reaction is generally complete in from 0.5 to 3 hours, dependingupon the amount of substrate employed. It is preferred, however, thatthe reaction be terminated after a period of two to three hours in orderto avoid excessive concentration of explosive hydroperoxide, in whichcase unreacted starting material is readily recovered and recycled tothe reactor.

\Advantageously, small amounts of the hydroperoxide corresponding to thedesired product may be introduced into the reaction medium to act as thereaction initiator. Thus, for example, when cumene is being oxidized, ithas been found to be advantageous to add a small amount of cumylhydroperoxide in order to initiate the reaction.

The resulting hydroperoxide product is readily recovered from thereaction medium by conventional methods. Thus, for example,hydroperovide may be conveniently recovered by isolating it as itssodium salt by addition of concentrated aqueous NaOH to the reactionproduct.

The hydroperoxides obtained by the process of this invention are highlyuseful in various important commercial applications. Thus, for example,when cumene is oxidized in accordance with the present invention, thereis formed a-cumyl hydroperoxide which, when reacted with an acid such assulfuric acid, is converted to industrially useful phenol and acetone inaccordance with the following reaction.

(3H5 (3H3 Q-r 02 CH3 CH3 Q-on CHsO-CH3 EXAMPLES 14 The following fourreactions were carried out in a 50 ml. reactor which was fitted with awater-cooled reflux condenser and immersed in a thermostated oil bathwhich was held at 105 C. The reactor was fitted with a hollow stirrershaft through which oxygen could be added and dispersed, and thereaction medium was rapidly stirred as the oxygen was added. Oxygenpressure was maintained at about 1 atmosphere by a rapid flow-through of60 mls. of oxygen per minute.

To this reactor was added, for each of the following runs, cumene (200mmoles), cumyl hydroperoxide promoter (1 mole percent), and as noted,various quantities of catalyst or, for sake of comparison, the separatecomponents of the catalyst system. The results obtained are reported asfollows in Table I:

It will be seen from the foregoing results that the rate f conversionprovided by the catalyst complex far exceeds the combined rates obtainedfrom each of the two separate catalyst components by a factor of fromthree to five times of what should be expected.

EXAMPLE 5 The procedure of Examples 1-4 is repeated, substituting 200mmoles of phenylcyclohexane for cumene. The catalyst consists of 20 mg.Cu Cl and 57 mg. pyridine. After four hours phenylcyclohexyll-hydroperoxide is obtained.

EXAMPLE 6 The procedure of Example 5 is repeated, substituting 200 moles 0f ethylbenzene for cumene. The catalyst consists of 10 mg. Cu Brand 55 mg. of quinoline. After three hours ethylbenzyl hydroperoxide isobtained.

EXAMPLE 7 The procedure of Example 5 is repeated, substitutingfi-sec.-butylnaphthalene for cumene. The catalyst consists of 20 mg. C11Cl and 60 mg. pyridine. After five hours fl-sea-butylnaphthalenehydroperoxide is obtained.

What is claimed is:

1. In a process for the oxidation of secondary and tertiary alkylaromatic hydrocarbons with oxygen or an oxygen-containing gas attemperatures of from to 130 C. in the presence of a catalyst to producethe corresponding hydroperoxide compounds, the imporvement whichcomprises oxidizing said alkyl aromatic hydrocarbons having the formulain which R is a lower alkyl group having from one to seven carbon atoms;R is hydrogen or a lower alkyl group having from one to six carbonatoms; R and R taken together, form a cycloalkyl ring having from fourto seven carbon atoms; and Ar is phenyl or naphthyl, in the presence ofa catalyst comprising a cuprous halide selected from the groupconsisting of cuprous chloride, cuprous bromide, and cuprous iodide, andan aromatic heterocyclic amine selected from the group consisting ofpyridine, quinoline, isoquinoline, triazine and pyrazine, wherein theratio of cuprous halide to amine is in the range of about 1 to parts byweight of said halide for each 100 parts of amine.

2. The process according to Claim 1 wherein the alkyl aromatichydrocarbon is cumene.

3. The process according to Claim 1 wherein the alkyl aromatichydrocarbon is ethylbenzene.

4. The process according to Claim 1 wherein the catalyst is cuprouschloride and pyridine.

5. The process according to Claim 1 wherein the temperature is in therange of from 90 to C.

6. The process according to Claim 1 wherein the oxidation is carried outin the presence of added hydroperoxide.

7. The process according to Claim 1 which comprises oxidizing cumene inthe presence of a catalyst comprising cuprous chloride and pyridine toobtain cumyl hydroperoxide.

8. The process according to Claim 1 which comprises oxidizingphenylcyclohexane in the presence of cuprous chloride and pyridine toobtain phenylcyclohexyl l-hydroperoxide.

9. The process according to Claim 1 which comprises oxidizingethylbenzene in the presence of cuprous bromide and quinoline to obtainethylbenzyl hydroperoxide.

10. The process according to Claim 1 which comprises oxidizingfl-secbutylnaphthalene in the presence of cuprous chloride and pyridineto obtain fi-secz-butylnaphthalene hydroperoxide.

References Cited UNITED STATES PATENTS 2,734,086 2/1956 Goppel et al260-6l0 B 2,430,864 1/1947 Farkas et a1. 260610 B 2,749,368 6/1956Fortuia et al. 2606l0 B BERNARD HELFIN, Primary Examiner W. B. LONE,Assistant Examiner

1. IN A PROCESS FOR THE OXIDATION OF SECONDARY AND TERTIARY ALKYLAROMATIC HYDROCARBONS WITH OXYGEN OR AN OXYGEN-CONTAINING GAS ATTEMPERATURES OF FROM 80* TO 130* C. IN THE PRESENCE OF A CATALYST TOPRODUCE THE CORRESPONDING HYDROPEROXIDE COMPOUNDS, THE IMPROVEMENT WHICHCOMPRISES OXIDIZING SAID ALKYL AROMATIC HYDROCAR: BONS HAVING THEFORMULA